By default CFD will use as many physical cores as exist on the machine. We do not leverage Hyper-Threading (or virtual cores). So if you have Hyper-Threading turned on, (assuming 4 core cpu) we would at most use 50% according to Windows. Windows will report 8 threads, 4 physical cores and 4 virtual.
We set 1 solver per real core. We do NOT solve on the GPU.
The status of your solver process is described in the message window; what messaging do you see there? Does the process fail during meshing? During solver setup? Execution? It would also help if you were to upload the .cfz file for internal review.